How to develope a pest list appropriate to vegetatively propagated plants in tissue culture

The word 'pest' here is as defined in the International Plant Protection Convention IPPC). It encompasses all harmful biotic agents ranging from viroids to weeds and Living Modified Organisms (LMOs).

The production of a pest list is essential to support and facilitate the movement of plant germplasm between countries. The production of such lists is in accordance with the International Plant Protection Convention (IPPC) principles of transparency and cooperation and helps importing countries assess the risk involved in the importation of the germplasm. Pest lists are simply lists of pests associated with a particular host or group of hosts. They may be related to any defined geographical are but most are global, regional or national in perspective.

When considering movement of germplasm in tissue culture the pest list can be narrowed down considerably to include only those organisms that present a risk in tissue culture material. These include viruses, viroids, phytoplasmas and latent and nutritionally demanding bacteria.

Pest list initiation

A pest list should be obtained when a decision has been made to import a plant commodity. The type of material to be imported and the perceived risk of contamination by pests associated with that material will govern the detail required in the list. Thus vegetative propagating material (e.g. potato tubers, cassava cuttings, banana setts) will present a high risk of transmitting a wide range of pests, seeds will present a lower risk and tissue culture material will present the lowest risk. The list should include all the pests that could be introduced with the plant material being imported (see the prioritisation of pests in a pest list document).

Although the information required will vary the information usually required includes:

Scientific name of the pest
Common name of the pest
Synonyms
Former names
Presence or absence in the importing country
Presence or absence in the exporting country
Distribution in importing country
Distribution in exporting country
Quarantine listing by relevant national and regional plant protection organisations

Information that may also be useful to include in the pest list includes:

Type of organism e.g. saprophyte/secondary pathogen/vector etc.
Notes on importance/risk of the pest
Plant part attacked
Symptoms
Likelihood of pest being carried on above ground plant parts
Likelihood of pest being carried on bare (soil free) roots
Likelihood of pest being carried with seed

At this stage it is useful to check with National Plant Protection Organisations of importing and exporting countries for existing pest lists for the plant host being imported as well as any synonyms of the host and closely related species if there is a chance of important pests switching hosts in the countries (or in-country areas) under consideration. Life stages of the plant host may also need to be considered.

Information sources

A first priority is to check plant disease records for the local and exporting country. Available scientific reports, annual and other reports from agricultural research stations and plant health authorities should also be consulted when available. Information may also be obtainable from the regional plant protection organisation covering the countries involved in the transfer of the plant material. Contact details for both national and regional plant protection organisations are available on the IPPC website (www. ippc.int). A list of regional plant protection organizations and their member countries is provided in Appendix 1. References to country and regional disease lists are available (Waller, 2002). However, it is then advisable to conduct a literature search even if pest lists are available for the plant host in the importing and exporting countries. The reason for this is that such lists are often infrequently updated and the pest situation can change within a short period of time (e.g. the increase in the number of recognised cassava mosaic geminiviruses in Africa over recent years).

Key information sources include American Phytopathological Society (APS), CAB abstracts, EPPO as well as more general internet searches (e.g. Google). Recent reviews or books dealing with pests of particular crops are especially useful and can be relatively easily located using internet searches of key words (e.g. viruses, cassava).

Useful starting points are the CABI Crop Protection Compendium and the CABI Forestry Compendium. Searching by host in these compendia can generate a crude list of pests associated with the host, which can then be augmented by searches on the EPPO PQR system. It is useful to include all known synonyms of the pest even if these have not been used for some time.

In some cases, it may be necessary to consider all organisms associated with a particular host and therefore, consideration must be given to whether it is a genuine pest, secondary pathogen or just an incidental record.

Searches on the APS website, CABI compendia and EPPO PQR will have generated a crude pest list. This needs to be divided into the following categories of organism: viruses and viroids, bacteria, phytoplasmas, fungi (including Oomycetes), arthropod pests and nematodes. Some organism groups may be ignored if it is considered that the risks associated with transmission in the material being shipped between countries is minimal (e.g. arthropod pests in tissue culture material). Special attention may need to be given to other groups which can readily be spread in this material (e.g, viruses, viroids, phytoplasmas and some bacteria in tissue culture material).

The ‘crude list’ will need to be augmented by specific searches for each pest group. Key sources for each group are listed below: